1. Field of the Invention
The present invention relates to an integrated heatable sensor for the purpose of measuring gas concentration.
Concentration measurements for different types of gases are performed in an increasing amount for both the living environment of man and industrial processes. Inflammable gases can be measured using sensors, which are operated with their surface temperature elevated above the ambient temperature. Inflammable gases in the ambient air are thereby oxidized on the sensor surface, and electrons released in the oxidization process alter the electrical conductivity of the sensor. Conventionally, this change in sensor resistance is converted into a voltage or current, whose magnitude is proportional to the gas concentration being measured.
2. Prior Art
In prior art constructions, the sensors are usually fabricated as separated sensor elements (or chips), which are bonded by electrical leads to the case encapsulating the sensor. In addition, the bonding leads act as springs, which support the sensor. Another method is to mount the sensor onto heat-insulating posts, while the electrical connections are bonded with thin conductors leads.
The first mentioned construction has two principal drawbacks. Firstly, the spring leads must be designed with a sufficient thickness in order to provide protection for the sensor against mechanical stresses, e.g., those caused by impact shocks. By contrast, a thicker lead conducts a great deal of heat away from the sensor element to thereby necessitate the application of increased heating power. Secondly, although mass production methods are being applied in the processing of the sensors, their fabrication into separated chips, the individual mounting of the chips into the sensor case, and the bonding of the chips to the attached electronics results in a complicated and expensive sensor manufacturing process.